LUBBOCK, Texas, Dec 8 (Reuters) - A San Antonio, Texas, school district has removed over 400 books from library shelves, works included on a list that a conservative state lawmaker has said may be inappropriate for children. The North East Independent School District said in an emailed statement on Wednesday that it is reviewing 414 books and that most would likely be returned to library shelves soon, following a review for age appropriateness. Reports of the review came as free speech advocates are raising concerns about an increase in calls to ban books. The district said the review came in response to concerns of parents and a demand by State Representative Matt Krause that all school districts in Texas identify whether their libraries contain any of nearly 850 books he listed as being potentially inappropriate. Most of the books address gender, sexual orientation or race.For us, this is not about politics or censorship, but rather about ensuring that parents choose what is appropriate for their minor children," said Aubrey Chancellor, the director of communications at North East Independent School District. She said the district is adding electronic tools that will let parents see what library books their children are accessing, and that some books may require parental permission for students to check out. Freedom of speech advocates such as Deborah Caldwell-Stone, director of the American Library Association"s office for intellectual freedom, are concerned. Caldwell-Stone said the effort to ban certain books from school libraries had long existed, but never had she seen so many people making the effort at the same time. She said conservative groups are putting out on social media lists of books they want banned. Parents in different parts of the country then take complaints to school officials, prompting reviews. "They"re targeting books that have given voice to folks who have been traditionally marginalized in our society, and, seemingly, encouraging the censorship of those books by school boards and libraries," Caldwell-Stone said. PEN America, which seeks to protect free expression, said Texas is at the epicenter of what it called a national political push by Republican lawmakers to demonize books on race, gender and sexual identity. Texas Governor Greg Abbott in November called on the state"s education regulatory agencies to investigate what he called pornographic books in school libraries. In October, State Representative Krause, as chair of the House Committee on General Investigating, notified the Texas Education Agency that his committee was beginning an investigation. Jonathan Friedman, director of free expression and education at PEN America, said the Texas efforts were deeply disturbing and part of what he called an unprecedented trend that has hit several states. Friedman said he"s seeing a wave of school districts caving to demands that they restrict access to books. "The trend is very clear. It"s a wide, sweeping effort to catch any kinds of book that deal with racism, sex and gender, regardless of the ways in which those books deal with the topics," Friedman said. Krause"s office and the Texas Education Agency did not respond to requests for comment. (This story was refiled to include hyphen in Caldwell-Stone"s name in grafs 7, 8 and 10.)